1. Field of the Invention
The present invention relates to an on-vehicle fuel property detection device to be mounted on automobiles, motorcycles, etc. and, more particularly, to an on-vehicle fuel property detection device using an optical fiber sensor.
2. Description of the Related Art
It is a recent trend that alcohol-blended fuel mixed with bio-ethanol has been increasingly used in place of the conventional gasoline. In this alcohol-blended fuel, however, because of difference in optimum ignition timing, A/F and the like depending upon the contained-ethanol concentration, it is essential that alcohol concentration contained in the fuel is accurately detected in order to make appropriate control by engine control computer, i.e., ECU (electronic control unit).
To cope with this, it has been proposed that an alcohol-gasoline mixture ratio is measured with the use of an optical liquid sensor in which a large-caliber glass optical fiber provided with a light-emitting element at one end and a light-receiving element at the other end is folded back, and this folded part is exposed into a liquid to be measured coming in contact therewith to act as a detector part, as is disclosed, for example, in the Japanese Patent Publication (unexamined) 236144/1990 (ref. page 3, left upper col., lines 3 to 15; FIG. 1).
Further, it has been proposed that a fuel refractive-index detection side is formed on each of plural elongated light pipes in which a refractive index changes from a perimeter toward a core, and floodlighting object is prepared on one end face of the light pipe and a light-receiving object on the other end face, whereby an alcoholic content in a fuel is detected, as is disclosed, for example, in the Japanese Patent Publication (examined) 10654/1994 (ref. page 3, left col., lines 4 to 35; FIGS. 1 to 3).
In the mentioned conventional on-vehicle fuel property detection devices utilizing the optical fiber sensor, since a bent part is necessarily formed in the optical fiber, in order to suppress a bend loss in the propagated light intensity at this bent part, it is essential to secure a certain level of bend R, which has been a problem in downsizing the sensor itself. Moreover, it is a matter of course that use of plural light pipes (optical fibers) brings about a further problem in view of cost reduction and improvement in productivity due to complication of structure of the device itself.